1. Field of the Invention
This invention relates to optical systems, and more specifically, to optical systems that incorporating a coherent interference in either the illumination path or a measurement path.
2. Description of the Related Art
Optical measurement systems, optical storage and retrieval systems and other optical systems may be limited by many factors, including illumination beam size, diffraction limit, detector noise, and resolution. The above-incorporated patent applications disclose techniques for enhancing the performance of a variety of optical systems and improving the resolution and sensitivity of optical technologies disclosed therein.
It would be further desirable to improve the performance of the systems disclosed in the above-referenced patent applications, as well as other optical systems, in order to further improve their performance. The above-referenced patent application xe2x80x9cMETHOD AND SYSTEM FOR CONTROLLING RESONANCE WITHIN A RESONATOR-ENHANCED OPTICAL SYSTEMxe2x80x9d, discloses a method and system for resonance control by a closed-loop feedback system via control of effective optical cavity length either by adjusting the operating wavelength, the propagation constant of a path within the resonator or by adjusting the physical cavity length.
However, in certain applications it may not be practical to use such a feedback loop, especially when the control mechanism is the illumination wavelength, as the wavelength must be controlled very precisely for resonators having substantial path length (necessary for resonators having a high Q-factor). The system phase accuracy requirement in some measurement applications requires the wavelength control to meet or exceed 0.1% of the wavelength. Further, the resonator further multiplies deviations in phase by the cavity length. With a resonator length of 1000xcex, phase control to 0.1% of the wavelength dictates control of the illumination wavelength to within 1 part per million, which is difficult or impossible to stably achieve while maintaining high speed operation by using a tunable illumination source and feedback loop.
Therefore, it would be desirable to provide an alternative method and system for measurement and resonator control that does not require a closed-loop continuous feedback system for adjusting cavity length or illumination wavelength.
The foregoing objectives are achieved in an optical system and method and apparatus for measurement and resonator control. The system includes a swept-wavelength optical illumination subsystem, an optical detection subsystem and a device for producing interference disposed in at least one optical path between the illumination system and the detection system. The device for producing interference may a standard interferometer, multi-beam interference device or an infinite beam interferometer such as an optical resonator.
The detection system further includes time-domain analysis stage that may be used to provide direct measurement output or measure resonant cavity length permitting open-loop adjustment of cavity length or interferometer phase. The output of the time-domain analysis stage may include information about the position of resonance or interference peaks, shape, width and height of peaks or other variations in the detected optical signal.
In particular, components of the time-domain analysis provide information about the changing resonant path length of the resonator, which may be a measurement function of the system, or may be used for adjusting the illumination wavelength or effective cavity length in an open-loop system.
The foregoing and other objects, features, and advantages of the invention will be apparent from the following, more particular, description of the preferred embodiment of the invention, as illustrated in the accompanying drawings.